1. Field of the Invention
The present invention relates to the sensing and identification of metal tokens or coins electronically. More particularly, it relates to method and apparatus for identifying a variety of currency coins of several countries with high reliability and without the need of reprogramming or readjustment. More particularly still, the apparatus is suitable for yielding unique digital codes each corresponding to a single coin or token sensed and identified by the present method.
2. Prior Art of the Invention
It is known to utilize size, shape and electrical properties of a coin for coin discrimination. For example, these characteristics affect the coupling between an excited coil and a detection coil in U.S. Pat. No. 3,373,856 granted Mar. 19, 1968 to Kusters et al. The induced voltage in the detection coil is rectified and the coin is accepted only if the rectified voltage lies between two preset levels.
In U.S. Pat. No. 4,432,447 granted Feb. 21, 1984 to Tanaka, essentially the same principle as above is utilised to sort coins. But, in addition, there is another coil (3) through which the coin passes, which coil forms the arm of an excited bridge circuit. The variable arm of the bridge is adjusted such that it is normally unbalanced, and is balanced only when the "true" coin is passing through the coil. The zero output of the bridge when balanced momentarily is the indication of the true coin. The circuit is thus tailored to discriminate between a true coin of a desired denomination and a particular coin similar in configuration to the desired coin.
U.S. Pat. No. 4,460,080 granted Jul. 17, 1984 to Howard, discloses coin validation apparatus utilising a coil formed in two halves, connected in series with one half on one side of the coin runway and the other half on the other side of the coin runway. Capacitors are connected to the coil to form a resonant tank circuit, and the effect of a coin on the inductance and loss factor of the coil is compared to reference values to determine coin validity.
U.S. Pat. 4,742,903 granted May 10, 1988 to Trummer, discloses several oscillator tank circuits having different natural frequencies ranging from 120 kHz to 247 kHz. The attenuators of the oscillator tank circuits are balanced by resistors, so that the high frequency voltage which the oscillator exhibits with each of the tank circuits have the same amplitude in the absence of a coin. The effect of the coin alloy on the low frequency test signal is greater, while the effect of the depth of embossing is smaller.
U.S. Pat. 4,895,238 granted Jan. 23, 1990, to Speas discloses a coin discriminator system for use in an electronic parking meter. A deposited coin is inserted in the electronic parking meter and a chute guides the deposited coin past an inductor. The deposited coin causes a momentary change in the value of inductance of the inductor. A phase lock loop electronic circuit has an input connected to the inductor and the phase lock loop electronic circuit. The correction signal compensates for the change in value of inductance of the inductor and has a wave shape unique to the deposited coin. A microprocessor receives the correction signal wave form for comparison to a plurality of predetermined wave shapes of a plurality of known coins to thereby identify the deposited coin. The plurality of predetermined wave shapes are stored in a memory connected to the microprocessor.